Embodiments of the present invention relate to systems, devices, and methods for compensating voluntary and other accommodation of patients during ocular diagnostic and treatment procedures. In particular, embodiments provide techniques for improving the accuracy of ocular aberration measurements and the development of vision correction treatments by evaluating accommodation in a patient.
An ocular wavefront measurement can change dramatically as the eye accommodates and the lens shape changes. This measurement change can be manifested in a Hartmann-Shack spot pattern as a pincushion effect. Current wavefront-based refractometers often derive a patient's total refraction, or total ocular aberration, from a single measurement under the assumption that accommodation has been effectively suppressed. Yet patients can experience some degree of instrument myopia when such measurements are taken, as the eye tends to accommodate inappropriately when viewing though an optical instrument. For example, when a patient looks through an optical instrument such as a refractometer or an aberrometer, the eye often responds by accommodating more than would be necessary for natural viewing. In some cases this excess accommodation, or instrument myopia, can be on the order of several diopters. As a result, the effect of instrument myopia can lead to an inaccurate measurement of refraction.
A variety of approaches have been proposed to eliminate instrument myopia. In some cases, a doctor may try to simulate the object being viewed, for example a viewing target, as far away from the patient as possible such that the target is closer to optical infinity. When an eye is gazing at a far distance the eye lens is thin and relaxed, and accommodation is reduced. Another technique that attempts to cause eye to relax the accommodation mechanism involves fogging. Fogging can involve adding a small amount of plus sphere power with a convex spherical lens, to provide a slight overcorrection. When the eye is optically fogged, vision becomes blurrier as the eye accommodates, and thus accommodation is discouraged. Additional techniques involve asking the patient to relax their vision. However many patients do not respond as desired to such approaches. Even when these accommodation-elimination techniques are implemented some instrument myopia may persist. What is more, it is often difficult to determine whether the eye is accommodated or not, particularly when a doctor or other instrument operator making such a determination is inexperienced.
What is needed are systems and methods for reducing the amount of instrument myopia present in the eye during an optical measurement. Moreover, improved techniques are desired for determining residual accommodation of the eye. Relatedly, there is a need for systems and methods that can accurately determine whether a patient's eye is accommodated, or the degree to which the patient's eye is accommodated. Embodiments of the present invention provide solutions to at least some of these problems.